1. Field of the Invention:
The present invention relates to an ignition system means for a rotary piston engine and, more particularly, an improvement of a dual type ignition system means for a rotary piston engine having a leading and a trailing ignition plug.
2. Description of the Prior Art:
A rotary piston engine such as the Wankel type is often equipped with two ignition plugs spaced along the rotational direction of the rotor for improving the engine performance. An ignition plug located at the leading side of the other ignition plug as seen in the rotational direction of the rotor is called a leading ignition plug while the other is called a trailing ignition plug, wherein the two ignition plugs are independantly operated by individual electric circuits. With regard to the rotary piston engines having the leading and trailing ignition plugs, it is known that the emission of noxious components, particularly HC and CO in the exhaust gases is substantially reduced by stopping or delaying the sparking operation of the trailing ignition plug in a certain operational condition of the engine. This improvement of the exhaust gas emmission is considered to be effective because when the sparking operation of the trailing ignition plug is stopped or delayed, the combustion of the fuel-air mixture in the engine combustion chamber is extended downstream into the exhaust manifold and the manifold reactor is thereby maintained at a high temperature thereby effecting a better recombustion of the uncombusted components contained in the exhaust gases, thus accomplishing a better overall combustion of the fuel. However, this method is effective only in a particular operating condition of the engine, which is generally the idling operation and a low load low speed operation except the engine breaking condition. In view of this feature, an ignition system means which operates in a manner to stop or delay the sparking operation of the trailing ignition plug in the idling and a low speed low load operation except the engine breaking condition, is proposed as disclosed in Japanese Patent publication No. 15523/73.
On the other hand, in order to comply with the regulations which are getting stricter with respect to the limit of NOx, it is contemplated to incorporate an exhaust gas recirculation system also in the rotary piston engine.
In experimental research with regard to rotary piston engines having leading and trailing ignition plugs and incorporating exhaust gas recirculation system, the inventor of the present invention noted that if the sparking operation of the trailing ignition plug is stopped or delayed while the exhaust gas recirculation above a certain relatively moderate ratio is performed, the engine performance and the drivability of the vehicle are substantially deteriorated.